WO2018114619A1

WO2018114619A1 - Electric gear pump

Info

Publication number: WO2018114619A1
Application number: PCT/EP2017/082890
Authority: WO
Inventors: Nello Medoro
Original assignee: Robert Bosch Gmbh
Priority date: 2016-12-22
Filing date: 2017-12-14
Publication date: 2018-06-28
Also published as: IT201600130258A1

Abstract

An electric gear pump comprising a gerotor that may rotate about an axis of rotation A, comprising an external spur rotor and an internal spur rotor arranged outside the external spur rotor; a stator having electrical windings arranged outside the gerotor; a bearing coupled to the stator internally; at least one magnetic structure integrated in the gerotor in such a way as to cause the gerotor to rotate when the electrical windings of the stator are supplied with current; in which the stator is divided into at least two annular portions which are complementary and independent of one another; the pump further comprises at least one elastic element acting on the annular portions and designed to compress the annular portions against the bearing.

Description

Title

ELECTRIC G EAR PU MP The present invention relates to an electric gear pump. In particular, the present invention relates to a gerotor electric gear pump.

The present invention also relates to a pump assembly comprising, in series: - a low-pressure pump (the abovementioned gerotor electric gear pump) for drawing fuel, preferably diesel, and for initial compression of the fuel; and

- a high-pressure pump, preferably with pumping pistons, for further compression of the fuel and for supplying the fuel at high pressure to an internal combustion engine.

The use of systems for supplying fuel, in particular diesel, to an internal combustion engine, which comprise a high-pressure pump for supplying the internal combustion engine, and a low-pressure pump for supplying fuel to the high-pressure pump, is already known. The high-pressure pump comprises at least one pumping piston moved by a shaft and housed in a cylinder supplied with fuel at low pressure. At least two different types of low-pressure pump for such systems currently exist. The first type comprises a gear pump which is driven by the same shaft as drives the pistons of the high-pressure pump. In particular, this gear pump may be a "gerotor" pump. As is known, the gerotor pump comprises an external spur rotor rotated by the shaft and housed inside an internal spur rotor. During rotation, the spurs of the external spur rotor engage with the spurs of the internal spur rotor, which has one more spur than the external spur rotor. The two rotors, rotating either absolutely or relatively, or relative to one another, pump fuel from an inlet, connected to the tank, to an outlet, connected to the high-pressure pump.

The second type of gear pump comprises gear pumps not driven by the shaft for driving the pumping pistons, but pumps driven electrically or electromagnetically. With this type of pump, in current gerotor pumps, at least one out of the internal spur rotor and the external spur rotor has magnetic or ferromagnetic modules, such as bundles of little plaques made of iron, which engage electromagnetically with a stator which is arranged outside of the internal spur rotor and comprises electrical windings. Usually, the internal spur rotor is made of sintered steel. In particular, it is currently common to house the magnetic modules, which usually have a parallelepiped structure, embedded directly in the internal spur rotor near the external surface thereof, or near the windings of the stator placed outside the internal spur rotor.

By supplying current to said windings, electromagnetic conditions are created such that the gerotor starts to rotate, pumping the fuel between the tank and the high-pressure pump.

In this type of gerotor electric gear pump, the stator with electrical windings, which may also be defined as an "electric motor" since it causes the gerotor to move, is placed at the same level as said gerotor so as to increase the electromagnetic interaction. This concentric arrangement of gerotor and stator currently requires the presence of a bearing placed between the external wall of the internal spur rotor of the gerotor and the stator. A high degree of precision in terms of mechanical machining regarding the geometric circularity of the external surface of the internal spur rotor coupled to said bearing is thus necessary.

The use of plastic, usually PEEK, is known for making the bearing, while the stator housing the windings is made of metal, usually steel. In particular, the bearing is coupled to the internal surface of the stator by surface interference.

Although gerotor electric gear pumps are widely used, the current versions of these pumps have a number of drawbacks.

In particular, the coupling between the bearing made of PEEK and the stator made of steel, as described above, is not guaranteed in all the thermal conditions in which the pump operates. To be specific, as is known, PEEK and steel have very different thermal expansion coefficients and therefore, for the same temperature difference, the bearing will undergo much greater deformation than the stator. This difference has a two-fold consequence. The first is that, at low temperatures, the bearing tends to shrink more than the stator, with the result that the bearing may become detached from the stator. In the event of high temperatures, the bearing tends to expand more than the stator. In such circumstances, the bearing may become compressed against the stator, a rigid steel body, to the extent that it is damaged or breaks owing to the internal tensions which are not released by corresponding widening.

In light of the known prior art, it is an aim of the present invention to produce an alternative gear pump, preferably an alternative gerotor electric gear pump.

In particular, it is an aim of the present invention to produce a gerotor electric gear pump which makes it possible to improve the corresponding prior art pumps described above, simply and economically, both from the functional viewpoint and from the structural viewpoint.

In accordance with these aims, the present invention relates to an electric gear pump comprising:

- a gerotor that may rotate about an axis of rotation A, comprising an external spur rotor and an internal spur rotor arranged outside the external spur rotor; - a stator having electrical windings arranged outside the gerotor;

- a bearing coupled to the stator internally, or to the internal surface thereof;

- at least one magnetic structure integrated in the gerotor in such a way as to cause the gerotor to rotate when the electrical windings of the stator are supplied with current.

In particular, according to the present invention

- the stator, which is annular in shape, is divided into at least two annular portions, which are complementary and independent of one another, about the axis A; and

- the pump further comprises at least one elastic element acting on the annular portions and designed to compress them against the bearing.

Advantageously, in this way the greater expansion of the bearing with respect to the stator, which happens when there is an increase in temperature, is not limited by a rigid structure. To be specific, the stator of the present invention is able to expand beyond its natural thermal expansion owing to the inclusion of the elastic element, and can thus accommodate the greater expansion of the bearing without any damage. Also in this way, including when assembled, when the elastic element is already acting on the portions of the stator to push them against the bearing, correct operation of the pump is thus ensured.

Preferably, when assembled, the annular portions making up the stator are separated from one another by at least one gap, for example in the form of an external split.

Advantageously, in this way, even in the event of a drop in temperature, the greater shrinkage of the bearing with respect to the stator does not affect correct operation of the pump. To be specific, the stator of the present invention can shrink beyond its natural thermal shrinkage owing to the inclusion of the elastic element which automatically causes the gap to be reduced until the internal surface of the annular portions presses against the bearing. Also in this way, correct operation of the pump is thus ensured.

According to various embodiments of the invention, the elastic element may be at least one spring having ends coupled to two adjacent annular portions, and designed to act in traction on the latter. Alternatively, the elastic element may be a ring or sleeve made of elastic material fitted in a stretched position around the annular portions, or a C-shaped element made of elastic material fitted in a stretched position around projecting portions of the annular portions, straddling the gap.

Advantageously, all of the above variants achieve the aim of providing the annular portions that make up the stator with inexpensive elements which are readily available on the market, and which are capable of performing the innovative functions of the invention described above.

According to a first embodiment of the invention, in which the elastic element is a traction spring, the stator is divided into two equal annular portions which, on one side, are separated by a gap and, on the other side, i.e. at the diametrically opposite point, are joined by a hinge having an axis of rotation parallel to the axis A. In this example, the traction spring is placed straddling the gap between the annular portions, in a position opposite the hinge.

According to another embodiment of the invention in which the elastic element is a traction spring, the traction spring is an annular spring centred on the axis A which extends along the whole of the external periphery of the annular portions.

According to another embodiment of the invention in which the elastic element is a traction spring, the stator is divided into two annular portions separated by two opposing gaps. In this case, two traction springs are placed straddling the gaps in diametrically opposite positions.

Preferably, the abovementioned traction springs, or indeed the alternative sleeve or ring made of elastic material, are housed in circumferential seats inside the annular portions.

Advantageously, in this way the invention does not require re-dimensioning of the rest of the components that make up the pump. Naturally, the present invention can be used both for a pump assembly for supplying fuel from a tank to an internal combustion engine which comprises, in series, an electric gear pump as described above and a high-pressure pump, and for just the stator as a possible spare part that may be used to improve the pumps currently used.

Further features and advantages of the present invention will become clearer from the description below of two non-limiting embodiments thereof, with reference to the figures in the attached drawings, in which:

- Figure 1 is a schematic view of an embodiment of a pump assembly for supplying fuel, preferably diesel, from a tank to an internal combustion engine, which comprises, in series, a low-pressure gear pump and a high-pressure pump with pumping pistons;

- Figure 2 is a schematic view of a low-pressure gerotor gear pump according to the prior art;

- Figure 3 is a schematic view along the axis of rotation A of the gerotor in an embodiment of the stator according to the present invention;

- Figure 4 is a schematic view of the stator of Figure 3 along the axis of rotation A of the gerotor coupled to the bearing, according to one embodiment of the invention;

- Figure 5 is a schematic view of the stator of Figure 3 along the axis of rotation A of the gerotor coupled to the bearing, according to another embodiment of the invention;

- Figure 6 is a schematic view of the stator of Figure 3 along the axis of rotation A of the gerotor coupled to the bearing, according to one embodiment of the invention; - Figure 7 is a schematic view of the stator of Figure 3 along the axis of rotation A of the gerotor coupled to the bearing, according to one embodiment of the invention.

Figure 1 is a schematic view of an embodiment of a pump assembly for supplying fuel, preferably diesel, from a tank to an internal combustion engine, which comprises, in series, a low-pressure pump and a high-pressure pump. In particular, Figure 1 shows a pump assembly 1 comprising:

- a low-pressure electric gear pump 4;

- a high-pressure pump 5;

- a low-pressure suction pipe 6 for supplying the fuel from the tank 2 to the electric gear pump 4;

- a low-pressure delivery pipe 7 for supplying the fuel from the electric gear pump

4 to the high-pressure pump 5;

- high-pressure delivery pipe 8 for supplying the fuel from the high-pressure pump

5 to the internal combustion engine 3.

In this example, the internal combustion engine 3 is shown only schematically and comprises a common manifold 17 fed by the high-pressure delivery pipes 8 and a plurality of injectors 18 (not shown) designed to spray and inject the fuel at high pressure into the cylinders of the internal combustion engine 3. In Figure 1, the high-pressure pump 5 is shown only schematically and comprises two pumping pistons 11 supplied with fuel at low pressure at supply valves 12 and connected to delivery valves 13 for supplying the fuel at high pressure to the engine 3. Figure 1 also shows a filter 10 arranged downstream of the low- pressure pump 4, a fuel measuring device 14 downstream of the filter 10, a relief valve 15 between the filter 10 and the fuel measuring device 14, a pressure limiting valve 19 connected to the manifold 17 and a valve 20 for delivering to the tank 2. The arrows shown in Figure 1 indicate the path of the fuel through the pump assembly 1.

Figure 2 shows a gerotor electric gear pump 4 according to the prior art. Said electric gear pump 4 comprises:

- a gerotor 9 that may rotate about an axis of rotation A, comprising an external spur rotor 21 and an internal spur rotor 22 arranged outside the external spur rotor 21; - a stator 25 made of metal and having seats 33 for housing electrical windings

26;

- a support base 24 for the gerotor 9; - a cover 27 that may be coupled to the base 24 in which the supply 6 and delivery 7 pipes are made at least partially;

- a bearing 28, made of PEEK and coupled to associated seals 16, between the stator and the gerotor 9, in particular the external surface of the internal spur rotor 22.

As can be seen in Figure 2, the internal spur rotor 22 has a magnetic structure 23 arranged near the bearing 28 so as to maximize the electromagnetic interaction with the windings 26 of the stator 25.

Figure 3 is a schematic view along the axis of rotation A of the gerotor in an embodiment of the stator according to the present invention. In particular, according to this example, the stator 25 is divided into two annular portions 30, or half shells, each of which has an external surface 31 and an internal surface 32. In the example shown, the external surface 31 is a continuous curved surface while the internal surface 32 comprises a plurality of curved sections spaced apart from one another and formed by the bases of radial rib elements which separate the housings 33 for the electrical windings (not shown). In use, the internal surface 32 presses against the bearing 28 in such a way as to ensure correct operation of the pump 4 and the external surface 31 of the portions 30 make up the established external surface of the stator 25.

Figure 4 is a schematic view of the stator of Figure 3 along the axis of rotation A of the gerotor coupled to the bearing, according to a first embodiment of the invention. According to the example of Figure 4, the stator 25 is divided into two annular portions 30 which, when assembled, on the one hand press against the bearing 28 via the internal surface 32 and, on the other hand, have two diametrically opposite separation gaps 36. Compression against the bearing 28 is ensured by the presence of two traction springs 29 mounted straddling the gaps 36 and having ends coupled to relative projecting portions on the external surface of the annular portions 30. If the bearing 28 contracts, the springs 34 act in traction, reducing the gaps 36 and bringing the internal surface 32 of the portions 30 back into contact with said bearing 28. On the contrary, if the bearing 28 expands, the springs allow the portions 30 to widen and thus accommodate said expansion.

Figure 5 is a schematic view of the stator of Figure 3 along the axis of rotation A of the gerotor coupled to the bearing, according to another embodiment of the invention. The difference with respect to the example of Figure 4 lies in the nature of the elastic elements. To be specific, in the example of Figure 5, the springs are replaced by C-shaped elements made of elastic material, fitted over projections and straddling the gaps 36.

Figure 6 is a schematic view of the stator of Figure 3 along the axis of rotation A of the gerotor coupled to the bearing, according to one embodiment of the invention. In this example, there is a single spring 29 arranged along the whole periphery of the external surface 31 of the annular portions 30. By fitting the spring 29 in a stretched state around the portions 30, it exerts the compression necessary in the direction of the bearing and at the same time allows the portions 30 to widen to accommodate the extra thermal expansion of the bearing 28 with respect to the stator 25.

Figure 7 is a schematic view of the stator of Figure 3 along the axis of rotation A of the gerotor coupled to the bearing, according to one embodiment of the invention. In this example, there is a hinge 35 joining the portions 30, which is diametrically opposite a spring 29 straddling the gap 36. Lastly, it is clear that amendments and variations may be made to the invention described herein without exceeding the scope of the attached claims.

Claims

1. An electric gear pump (4) comprising:

- a gerotor (9) that may rotate about an axis of rotation (A), comprising an external spur rotor (21) and an internal spur rotor (22) arranged outside the external spur rotor (21);

- a stator (25) having electrical windings (26) arranged outside the gerotor (9);

- a bearing (28) coupled to the stator (25) internally,

- at least one magnetic structure (23) integrated in the gerotor (9) in such a way as to cause the gerotor (9) to rotate when the electrical windings (26) of the stator (25) are supplied with current;

in which

- the stator (25) is divided into at least two annular portions (30) which are complementary and independent of one another;

- the pump (4) further comprises at least one elastic element (29) acting on the annular portions (30) and designed to compress the annular portions (30) against the bearing (28).

2. Pump as claimed in Claim 2, in which, when assembled, the annular portions (30) are separated from one another by at least one gap (36).

3. Pump as claimed in Claim 1 or 2, in which the elastic element (29) is at least one spring having ends coupled to two adjacent annular portions (30), and designed to act in traction on the annular portions (30).

4. Pump as claimed in Claim 3, in which the stator (25) is divided into two annular portions (30) which, on one side, are separated by a gap (36) and, on the other side, are joined by a hinge (35), the traction spring (29) being placed straddling the gap (36).

5. Pump as claimed in Claim 3, in which the traction spring (29) is an annular spring centred on the axis (A)

6. Pump as claimed in Claim 3, in which the stator (25) is divided into two annular portions (30) separated by two opposing gaps (36), two traction springs (29) being placed straddling the gaps (36).

7. Pump as claimed in Claim 2, in which the elastic element (29) is a ring or sleeve made of elastic material fitted in a stretched position around the annular portions (30).

8. Pump as claimed in any one of the preceding claims, in which the elastic element (29) is housed in circumferential seats inside the annular portions (30).

9. Pump as claimed in Claim 2, in which the elastic element (29) is a C- shaped element made of elastic material fitted in a stretched position around projecting portions (34) of the annular portions (30), straddling the gap.

10. A pump assembly for supplying fuel from a tank (2) to an internal combustion engine (3); the pump assembly (1) comprising, in series, a low- pressure electric gear pump (4) and a high-pressure pump (5); in which the electric gear pump (4) is produced according to any one of the preceding claims.